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Conditional Inner Join

Posted on 2004-04-05
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Last Modified: 2012-06-21
I have two tables that I can link together with a common field.  However there is an instance where there could be more than one value in the second field.  For example..

Field1        Field2        Field3
1234         555            
3321         865
2956         362           GODNAT
2956         363           HEJ


I would like to be able to link on Field1 unless Field3 is pupulated, and then use the value in Field2 in my results.

Any suggestions would be a huge help!

/Atropa
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Question by:Atropa
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8 Comments
 
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Expert Comment

by:vc01778
ID: 10760380
You can do this:

select ...  from
table1 join
 (select  case when field3 is null then field1 else field2 end field_x, .., from table2)  t2 on table1.id=t2.field_x


...here field_x is a field computed from field1/field2/field3.


VC
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Author Comment

by:Atropa
ID: 10760522
okay, so here is what I have yet I am getting a message saying..
Incorrect syntax near the keywork 'ON'.

FROM bbadger.tblcommhmo2
      INNER JOIN dbo.tbl_IDXeGrps
      ON bbadger.tblcommhmo2.XMAP_IDX_HP_NM = dbo.tbl_IDXeGrps.HealthPlan
      INNER JOIN
            (SELECT CASE
            WHEN schandler.tblNWOC_IDX_PC_XMAP.PLANCODE_ORG IS NULL
            THEN schandler.tblNWOC_IDX_PC_XMAP.NWOC_PC
            ELSE schandler.tblNWOC_IDX_PC_XMAP.PLANCODE_ORG
            END Link_Field
            FROM schandler.tblNWOC_IDX_PC_XMAP)
            ON bbadger.tblcommhmo2.IDX_PLANNUMBER = schandler.tblNWOC_IDX_PC_XMAP.Link_Field

schandler.tblNWOC_IDX_PC_XMAP is the field mentioned above.  I have never used a case statement in SQL only VB so I am not fully aware of the syntax.
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Accepted Solution

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vc01778 earned 500 total points
ID: 10760556
It should be:

FROM bbadger.tblcommhmo2
     INNER JOIN dbo.tbl_IDXeGrps
     ON bbadger.tblcommhmo2.XMAP_IDX_HP_NM = dbo.tbl_IDXeGrps.HealthPlan
     INNER JOIN
          (SELECT CASE
          WHEN schandler.tblNWOC_IDX_PC_XMAP.PLANCODE_ORG IS NULL
          THEN schandler.tblNWOC_IDX_PC_XMAP.NWOC_PC
          ELSE schandler.tblNWOC_IDX_PC_XMAP.PLANCODE_ORG
          END Link_Field
          FROM schandler.tblNWOC_IDX_PC_XMAP)  as XYZ
          ON bbadger.tblcommhmo2.IDX_PLANNUMBER = XYZ.Link_Field


VC
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Expert Comment

by:Anthony Perkins
ID: 10760568
You are missing the alias for the derived table as vc suggested:

  FROM schandler.tblNWOC_IDX_PC_XMAP) t2
          ON bbadger.tblcommhmo2.IDX_PLANNUMBER = t2.tblNWOC_IDX_PC_XMAP.Link_Field
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Expert Comment

by:Anthony Perkins
ID: 10760570
vc (as always) has it right.
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LVL 11

Expert Comment

by:vc01778
ID: 10760577
I assume you also want to select something from the derived table besides link_field ?  If so,  the column names will need to be qualified with the same alias (XYZ in this case).


VC
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Expert Comment

by:vc01778
ID: 10760589
@acperkins


Thank you ,  but not always ;)

VC
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Author Comment

by:Atropa
ID: 10760615
Thank you for ending my 3 hour long misery.  Now I can go to sleep in peace!  /Atropa
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